[cctalk] Re: interlace [was: NTSC TV demodulator ]

On May 20, 2024, at 10:06, CAREY SCHUG &lt;sqrfolkdnc(a)comcast.net&gt; wrote: Wayne, you must be one of those thirty-something techies from another thread. for those of us in our 60s and 70s,.... setup mode? huh? old TVs and monitors were purely analog. No on-screen displays and non-volatile memory bytes for setup. adjustments for size and position were rheostats. interlace (on TVs) was because the incoming sigonal started SLIGHTLY later for the interlaced frame and the horizontal sync was slightly different (advanced?) on the incoming signal relative to the vertical sync. With digital, the conversion of the analog input to digital for the display has to start recording only half the first line. and whatever conversion there is because on the analog display, the scan line is at a slight angle, lower on the right, so the interlaced frame starts at the same vertical height, in the middle, as the other frame started on the left side. so, just curious. how do digital TVs (and monitors) work? I presume the dots are a rectangle, not sloping down to the right, no half a line at the top and bottom. Do they just assume the brain can't tell that (for the converted old analog tv signal) the image therefor slopes UP very slightly to the right from what it "should" be? and the top line is blank on the left side because that is the interlace frame? <pre>--Carey</pre> > On 05/20/2024 11:46 AM CDT Wayne S via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: > > > IIRC, didn’t most older pc monitors have a setup mode where one of the options was interlace or non-interlace. > > > Sent from my iPhone > >>> On May 20, 2024, at 09:35, Paul Koning via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: >> >> I think you have that backwards. >> >> TVs use interlace. Older PC displays may do so, or not; typically the 480 line format was not interlaced but there might be high resolution modes that were. The reason was to deal with bandwidth limitations. >> >> Flat panel displays normally support a pile of input formats, though only the "native" format (the actual line count matching the display hardware) is directly handled, all the others involve reformatting to the native format. That reformatting generally results in some loss of display quality, how much depends on how well the relevant hardware is designed. And interlaced formats are often supported not just for the VGA input (if there is one) but also for DVI/HDMI inputs. To get the accurate answer you have to check the specification sheet. >> >> paul >> >>> On May 20, 2024, at 12:13 PM, CAREY SCHUG via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: >>> >>> This may have been covered before, VERY early in this tread. >>> >>> I think I tried a game on a flatscreen, and had issues. I don't know if it applies to the radio shack Color Computer, the interest of the original poster. >>> >>> many games and entry pcs with old style tv analog format, don't interlace, and tube TVs nearly all (except maybe a few late model high end ones?) are fine with that, but I seem to recall that most or all digital/flat screen can't deal with non-interlace. >>> >>> <pre>--Carey</pre> >>